The use and mechanism of control agents for free radical polymerization is now generally known (see U.S. Pat. No. 6,153,705, WO 98/01478, WO 99/35177, WO 99/31144, WO 98/58974, and U.S. Patent Application 20040073042). However, there remains a need for new agents that may lead to a commercially viable process. In particular, control agents that work to control the polymerization of vinyl monomers are of interest. Typical examples of vinyl monomers include styrene, (meth)acrylates, (meth)acrylamides, and the like. The control agents described in WO 98/01478, WO 99/35177, WO 99/31144, WO 98/58974, and U.S. Patent Application 20040073042 generally operate according to a reversible addition-fragmentation transfer mechanism, which confers a “living” character to the free radical polymerization of ethylenic monomers.
In general the commercial potential of controlled free radical polymerization (CFRP) is enormous. It has always been desirable to prepare well-defined homogeneous, block, graft, gradient, star, comb, end-functional and many other materials by free radical means under mild reaction conditions. This rapidly emerging ability via CFRP techniques is perhaps the most likely reason we are currently witnessing an explosion in academic and industrial interest with thousands of papers and hundreds of patents over the last five years. Recent estimates indicate that CFRP could easily affect a market of $20,000,000,000 per year across a very wide range of polymer applications.
U.S. Patent Application 20040073042 discloses control agents that have an O—N bond covalently bonded to a thiocarbonyl moiety. In some embodiments of U.S. Patent Application 20040073042 the control agents are of the general formula:
wherein R1 is generally any group that is sufficiently labile to be expelled as its free radical form; R2 and R3 are each independently selected from the group consisting of hydrogen, hydrocarbyl, substituted hydrocarbyl, heteroatom-containing hydrocarbyl, and substituted heteroatom-containing hydrocarbyl, and combinations thereof, and optionally, R3 combines with R2 to form a ring structure, with said ring having from 3 to 50 non-hydrogen atoms.
In an alternative embodiment of U.S. Patent Application 20040073042 the control agent is a ring structure, which upon ring opening may form a multi-functional control agent. These cyclic control agents are of the structural formula:
wherein R1 is a bifunctional moiety that is sufficiently labile to be expelled as its free radical form; wherein R2 and R3 are each independently selected from the group consisting of hydrogen, hydrocarbyl, substituted hydrocarbyl, heteroatom-containing hydrocarbyl, and substituted heteroatom-containing hydrocarbyl, and combinations thereof, and wherein R3 can optionally combine with R2 to form a ring structure, with said ring having from 3 to 50 non-hydrogen atoms.